What made you change to a 6SN7 preamp?

In building preamp amplifiers, the 6SN7 based tube in general is a warmer sound, more relaxed presentation, more dimensional soundstage with real mid-range beauty.  That being said, the 6DJ8/6922 is generally more dynamic, faster, better clarity, and more slam.  It is a more upfront presentation.

6DJ8s were not designed for audio and have trouble with microphonics. I find it far easier to find a low microphonic 6SN7. Microphonics tend to add an iridescence to the sound that is distortion, so despite the nice linearity of the 6DJ8 I learned to stay away from them.

@phantom_av    That's four less than my MP-1. Wonder why.

The MP-1 uses 6 6SN7s and 8 12AT7s.

After having microphonic issues with some 6SN7s I got lucky and got all excellent, quiet NOS Sylvania 6SN7s and great Mil spec 12AT7s for the phono stage. The improvement in SQ was dramatic and huge.

Brent Jesse and other tube suppliers do not have what private horders have.

If you can, find a horder.

I upgraded from a Cary SLP 90 (12AU7) to a Cray SLP 05 (6SN7) because 1) it was high time for a preamp upgrade, and 2) because Cary had one on their preowned page & I thought that the price was right.

I still don't think I have enough ear time into it to understand the pros and the cons

I am also still running with the Electro Harmonix tubes that came with it, and I have no doubt that those need to be upgraded, but there is so much out there I am overwhelmed with choices (so I have still done nothing)..

Brent Jesse and other tube suppliers do not have what private horders have.

What do you mean by this, I've had better luck buying tubes from vintage tube service than private sellers. Andy at vintage tube service won't sell you microphonic tubes.